Dehydration



I Patented July-1,1931

PATENT ori ce wrmmmn BILT Z, OF-EANOVEB, GERMANY, ASSIGN'OB TO I.FARBENIND'USTRIE AK- TIENGESELLSOHAFT, F

nnmznna'rron J I I I 1 110 Drawing. Appgllcation filed January 3, 1929,Serial No. 330,132, and in Germany May 1,4, i927.

This invention relates to improvements in 1 the dehydration of solidsubstances such as oxides having a content of water, 'for examplehydrogels or hydrates, or such as are moist- 8 vor are swollen by theabsorption ofwater with liquid ammonia, for example or by a contentthereof, these materials, being equivalents for the purposes of thepresent invention. I 7 Apart from the dehydration of solid substances byevaporation of the water contained therein, it is already known toreplace the water contained in solid substances to be.

dried by means of liquids, which can be more easily removed thanwater,"for exam 1e, on account of their higher. volatility. lcohol andacetone have, for example, been employed .for this purpose.

I have now found that ammonia, which has been liquefied by cooling or bythe application of pressure orboth, dissolves water to such a highdegree, even at temperatures below 0C., that solid sustances havin a.content of water, such for example as bydrogels or hydrates, or such asare moist or are swollen by a content-of water, for instance hydrogelsof silicic acid, or oxide of silicon, can be dehydrated by being)treated y being washed or extracted therewith. The term dehydrationincludes both drying and the removal of chemically bound water.

My process has the advantage that (a) the said dehydration may becarried out at very low temperatures down to about 80 below zero C. thepoint of solidification of ammonia), b) that the dehydration agentemployed according to the process of my invention is gaseous undernormal conditions of temperature and pressure and that the main portionthereof can "be removed from the.

solid to be dried without the employment of elevated temperature, bysimple evaporation,

and finally (c) that according to the process of my inventiontheoriginal physical and chemical structure of the material to be driedremains substantially unchanged.

The rocess according to y invention may be earned out under any suitableconditionsof temperature and pressure, at which ammonia is liquid. Thedehydration may for V introduction of liquid ammonia.

The following example will further illus- I .trate how my invention maybe carried out in practice, but the invention is not limited thereto.

. Example JA moist hydrogel of silicic acid is intro--FBANKFORT-ON-THE-MAIN, GERMANY, A CORPORATION O1 duced' into a closedfunnel vessel provided with a filter plate. Gaseous ammonia isintroduced into the funnel vessel in an amount suflicient to saturatethe water contained in portion of the water is thereupon filtered ofl?by suction. Thehydro'gel is thereupon covammonia in the said funnelvessel or .by the The am-' monia is thereupon pressed off from thehydrogel, preferably by means of the pres- .sure set up by the vapors ofthe liquid a1 n-- monia itself, or by. suction, and the operation isrepeated so often until the liquid ammonia leaves the filter entirelyfree from water. The small portion of the drying agent still thehydrogel with ammonia, and the first end by liquid ammonia, either byliquefying present in the material to be dried may be removed byevaporation.

A silicic hydrogel, prepared as described by J. Andersen in the.Zeitschrift fiir Physikalische Cheniie, vol. 88, page 191 (1914),-

when dried with liquid ammonia according to the process described in theabove example contains only 6.5 per cent of water, whereas a hydrogelsimilarly prepared but subjected to ageing when dried in the same mannercontains only. 5.7 per cent of water. The preparations thus obtainedare-very light loose powders. During the production of the dry gelsaccording to the manner described," these are never subjected to atemperaturehigher'than78.5 below zero 0., in the drying process proper.

According to the methods which have hitherto been employed in thedehydration of hydregels ofsilicic acid very high temperatures of 1p toabout 300 C. had to be emloyed in order to obtain a gel containing tween2 and 10 per cent of water. What Iclaim is: 1 1. A process for thedehydration of a solid oxide containing water which comprises treatingthe said oxide with liquid ammonia.

2. A pnocess for the dehydration of a hy- 4 drogel of silicic acid,which comprises treating the said hydrogel with liquid ammonia. 3'. Aprocess for the dehydration of a hydrogel'oi silicic acid, which comrises extracting the water from the said 11 ogei by means of liquidammonia.

4 A process for the dehydration of a hydrogel of silicic acid, whichcomprises contmuously and automatically extracting the I water from thesaid hydrogel by means of liquid ammonia.

In testlmony whereof I have hereunto'set my hand. v

" WILHELM BILTZ.

